This invention relates to an apparatus and method for making barrier-coated polyesters, preferably barrier coated polyethylene terephthalate (PET) and articles made therefrom. Preferably the barrier-coated PET takes the form of preforms having at least one layer of a barrier material and the bottles blow-molded therefrom.
The use of plastic containers as a replacement for glass or metal containers in the packaging of beverages has become increasingly popular. The advantages of plastic packaging include lighter weight, decreased breakage as compared to glass, and potentially lower costs. The most common plastic used in making beverage containers today is PET. Virgin PET has been approved by the FDA for use in contact with foodstuffs. Containers made of PET are transparent, thin-walled, lightweight, and have the ability to maintain their shape by withstanding the force exerted on the walls of the container by pressurized contents, such as carbonated beverages. PET resins are also fairly inexpensive and easy to process.
Despite these advantages and its widespread use, there is a serious downside to the use of PET in thin-walled beverage containers: permeability to gases such as carbon dioxide and oxygen. These problems are of particular importance when the bottle is small. In a small bottle, the ratio of surface area to volume is large which allows for a large surface for the gas contained within to diffuse through the walls of the bottle. The permeability of PET bottles results in soft drinks that go xe2x80x9cflatxe2x80x9d due to the egress of carbon dioxide, as well as beverages that have their flavor spoiled due to the ingress of oxygen. Because of these problems, PET bottles are not suitable for all uses desired by industry, and for many of the existing uses, the shelf-life of liquids packaged in PET bottles is shorter than desired.
U.S. Pat. No. 5,464,106 to Slat, et al, describes bottles formed from the blow molding of preforms having a barrier layer. The barrier materials disclosed are polyethylene naphthalate, saran, ethylene vinyl alcohol copolymers or acrylonitrile copolymers. In Slat""s technique, the barrier material and the material to form the inner wall of the preform are coextruded in the shape of a tube. This tube is then cut into lengths corresponding to the length of the preform, and is then placed inside a mold wherein the outer layer of the preform is injected over the tube to form the finished preform. The preform may then be blow-molded to form a bottle. The drawbacks of this method are that most of the barrier materials disclosed do not adhere well to PET, and that the process itself is rather cumbersome.
A family of materials with good barrier characteristics are those disclosed in U.S. Pat. No. 4,578,295 to Jabarin. Such barrier materials include copolymers of terephthalic acid and isophthalic acid with ethylene glycol and at least one diol. This type of material is commercially available as B-010 from Mitsui Petrochemical Ind. Ltd. (Japan). These barrier materials are miscible with polyethylene terephthalate and form blends of 80-90% PET and 10-20% of the copolyester from which barrier containers are formed. The containers made from these blends are about 20-40% better gas barriers to CO2 transmission than PET alone. Although some have claimed that this polyester adheres to PET without delamination, the only preforms or containers disclosed were made with blends of these materials.
Another group of materials, the polyamine-polyepoxides, have been proposed for use as a gas-barrier coating. These materials can be used to form a barrier coating on polypropylene or surface-treated PET, as described in U.S. Pat. No. 5,489,455 to Nugent, Jr. et al. These materials commonly come as a solvent or aqueous based thermosetting composition and are generally spray coated onto a container and then heat-cured to form the finished barrier coating. Being thermosets, these materials are not conducive to use as preform coatings, because once the coating has been cured, it can no longer be softened by heating and thus cannot be blow molded, as opposed to thermoplastic materials which can be softened at any time after application.
Another type of barrier-coating, that disclosed in U.S. Pat. No. 5,472,753 to Farha, relies upon the use of a copolyester to effect adherence between PET and the barrier material. Farha describes two types of laminates, a three-ply and a two-ply. In the three-ply laminate, an amorphous, thermoplastic copolyester is placed between the barrier layer of phenoxy-type thermoplastic and the layer of PET to serve as a tie layer to bind the inner and outer layers. In the two-ply laminate, the phenoxy-type thermoplastic is first blended with the amorphous, thermoplastic copolyester and this blend is then applied to the PET to form a barrier. These laminates are made either by extrusion or by injection molding wherein each layer is allowed to cool before the other layer of material is injected.
PCT Application Number PCT/US95/17011, to Collette et al., which was published on Jul. 4, 1996, describes a method of cooling multilayer preforms. The disclosed apparatus comprises a rotary turret having multiple faces, each face carrying an array of cores. The cores are inserted into corresponding mold cavities. Multiple melt streams are brought together and coinjected into each cavity to form a multilayer preform on each core. After the preform is injected, the cores are removed from the cavities and the turret is rotated, presenting a new set of cores to the mold cavities. The just-injected cavities remain on the cores cooling while preforms are formed on other arrays of cores. The drawbacks of the Collette application include that coinjection results in preforms that are inconsistent and have unpredictable layering. Thus, distribution of barrier materials in such a preform would be unpredictable and would result in a preform having unreliable barrier properties.
Since PET containers can be manufactured by injection molding using only a single injection of PET, manufacture is relatively easy and production cycle time is low. Thus, PET containers are inexpensive. Even if known barrier materials can be bonded to PET to create a saleable container with reliable barrier properties, methods and apparatus for making such containers within a competitive cycle time and cost have not been devised. Production cycle time is especially important because a lower cycle time enables a manufacturer to make more efficient use of its capital equipment. Thus, low cycle time enables higher volume and less expensive production of containers. Cost-effective production would be necessary to develop a viable alternative to monolayer PET containers.
Thus, the need exists for an apparatus and method for making barrier-coated PET preforms and containers which are economical, cosmetically appealing, easy to produce, and have good barrier and physical properties remains unfulfilled.
This invention relates to methods and apparatus for making PET articles having coated upon the surfaces thereof one or more thin layers of thermoplastic material with good gas-barrier characteristics. The articles of the present invention are preferably in the form of preforms and containers.
In an aspect of the present invention there is provided a barrier coated preform comprising a polyester layer and a barrier layer comprising barrier material, wherein the polyester layer is thinner in the end cap than in the wall portion and the barrier layer is thicker in the end cap than in the wall portion.
In another aspect of the present invention there is provided a method for making a barrier coated polyester article. A polyester article with at least an inner surface and an outer surface is formed by injecting molten polyester through a first gate into the space defined by a first mold half and a core mold half, where the first mold half and the core mold half are cooled by circulating fluid and the first mold half contacts the outer polyester surface and the core mold half contacts the inner polyester surface. Following this, the molten polyester is allowed to remain in contact with the mold halves until a skin forms on the inner and outer polyester surfaces which surrounds a core of molten polyester. The first mold half is then removed from the polyester article, and the skin on the outer polyester surface is softened by heat transfer from the core of molten polyester, while the inner polyester surface is cooled by continued contact with the core mold half. The polyester article, still on the core mold half is then placed into a second mold half, wherein the second mold half is cooled by circulating fluid. In the coating step, the barrier layer comprising barrier material is placed on the outer polyester surface by injecting molten barrier material through a second gate into the space defined by the second mold half and the outer polyester surface to form the barrier coated polyester article. The second mold half is then removed from the barrier coated article and then the barrier coated article is removed from the core mold half. The barrier materials used in the process preferably comprise a Copolyester Barrier Materials, Phenoxy-type Thermoplastics, Polyamides, polyethylene naphthalate, polyethylene naphthalate copolymers, polyethylene naphthalate/polyethylene terephthalate blends, and combinations thereof.
In a further aspect of the present invention, there is provided a method of making and coating preforms. The method begins by closing a mold comprising a stationary half and a movable half, wherein the stationary mold half comprises at least one preform molding cavity and at least one preform coating cavity and the movable mold half comprises a rotatable plate having mounted thereon a number of mandrels equal to the sum of the number of preform molding cavities and preform coating cavities. The remaining steps comprise: injecting a first material into the space defined by a mandrel and a preform molding cavity to form a preform having an inner surface and an outer surface; opening the mold; rotating the rotatable plate; closing the mold; injecting a second material into the space defined by the outer surface of the preform and the preform coating cavity to form a coated preform; opening the mold; removing the coated preform.
In accordance with a preferred embodiment having features in accordance with the present invention, an apparatus for injection molding multilayer preforms is provided. The apparatus comprises first and second mold cavities in communication with first and second melt sources, respectively. A turntable is provided and is divided into a plurality of stations, with at least one mold core disposed on each station. The turntable is adapted to rotate each station to a first position at which a core on the station interacts with the first mold cavity to form a first preform layer, then to a second position at which the core interacts with the second mold cavity to form a second preform layer. Finally, the turntable is further adapted to rotate the station to at least one cooling position, at which the molded preform remains on the core to cool.
In accordance with another preferred embodiment having features in accordance with the present invention, a mold apparatus for injection molding multilayer preforms is provided. The mold apparatus has a first mold body which is adapted to fit about a mold core to define a first layer cavity therebetween, a first gate area, and is in communication with a first melt source. A second mold body is adapted to fit about a first preform layer disposed on the mold core to define a second layer cavity therebetween, has a second gate area, and is in communication with a second melt source. At least one of the gate areas has Ampcoloy high-conductivity alloy metal inserts disposed therein.
In accordance with another preferred embodiment having features in accordance with the present invention, a mold apparatus for injection molding multilayer preforms is provided. The mold apparatus has a first mold body which is adapted to fit about a mold core, defining a first layer cavity therebetween. The first layer cavity has a base end and a main body. The first mold body is in communication with a first melt source and has a first gate area adjacent the base end of the first layer cavity. A thickness of the cavity at the base end is less than the thickness of the main body of the cavity. The mold apparatus also has a second mold body, which is adapted to fit about a first preform layer disposed on the mold core, defining a second layer cavity therebetween. The second mold body is in communication with a second melt source and has a second gate area.
In accordance with yet another preferred embodiment having features in accordance with the present invention, a mold for injection molding multilayer preforms is provided. The mold has a mandrel and first and second cavities. The mandrel is hollow and has a wall of substantially uniform thickness. A coolant supply tube is disposed centrally within the hollow mandrel to supply coolant directly to a base end of the mandrel. The first cavity has a gate for injecting molten plastic. A gate area of the cavity has an insert of material having greater heat transfer properties than the majority of the cavity.
In accordance with a further preferred embodiment having features in accordance with the present invention, a method for improving injection mold performance is provided. The method includes forming an opening in a wall of a mold cavity. The opening is sized and adapted so that molten plastic will not substantially enter the opening. A passageway is formed connecting the opening to a source of air pressure. The method further includes providing a valve between the opening and the source of air pressure.
In accordance with another preferred embodiment having features in accordance with the present invention, a method for injection molding and cooling a multilayer preform is provided. The method includes the steps of providing a mold core disposed on a turntable and having an internal cooling system, rotating the turntable so that the core is aligned with a first mold cavity, engaging the core with the first mold cavity, and injecting a melt to form a first preform layer. The first preform layer is held within the mold cavity to cool until a skin is formed on a surface of the layer, but an interior of the layer remains substantially molten. The core is then removed from the first mold cavity while retaining the molded preform layer on the core and the turntable is rotated so that the core is aligned with a second mold cavity. The core is engaged with the second mold cavity and a melt is injected to form a second preform layer on top of the first preform layer. The core is removed from the second mold cavity while retaining the molded preform on the core and the turntable is rotated so that the core and preform are in a cooling position during which the preform cools upon the core. The preform is eventually removed from the core.
In accordance with one aspect of the present invention, there is provided a laminate comprising at least one layer of polyethylene terephthalate directly adhered to at least one layer of barrier material. The polyethylene terephthalate has an isophthalic acid content of at least about 2% by weight. Barrier materials used include Copolyester Barrier Materials, Phenoxy-type Thermoplastics, Polyamides, polyethylene naphthalate, polyethylene naphthalate copolymers, polyethylene naphthalate/polyethylene terephthalate blends, and combinations thereof. In preferred embodiments, the laminate is provided in the form of preforms and containers.
In accordance with a further aspect of the present invention, there is provided a preform comprising at least two layers, wherein the first layer is thinner in the end cap than in the wall portion and the second layer is thicker in the end cap than in the wall portion. The first layer comprises polyethylene terephthalate having an isophthalic acid content of at least about 2% by weight and the second layer comprises a barrier material. Barrier materials used include Copolyester Barrier Materials, Phenoxy-type Thermoplastics, Polyamides, polyethylene naphthalate, polyethylene naphthalate copolymers, polyethylene naphthalate/polyethylene terephthalate blends, and combinations thereof.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described hereinabove. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.